1. Field of the Invention
The present invention relates to a technology for controlling a wiper apparatus for use ir a vehicle, and more particularly to a technology advantageously applied to a wiper apparatus in which a pair of wiper blades move in an opposing fashion.
2. Related Art Statement
There are two types of controlling manners in wiper blades. One of them is a parallel type in which a pair of wiper blades are driven while keeping substantially equidistant position between the blades. The other of them is an opposing type in which the pair of wiper blades are controlled to move in an opposing fashion. That is, when one of the blades moves to the center of the front glass the other of the wiper blades also moves to the center of the front glass while one moves away from the center the other is also moves away from the center. In a wiper apparatus of the opposed wiping type, rotation centers of wiper arms are respectively positioned at left and right ends of the front glass and wiper blades move from both sides of the front glass toward the center thereof.
The wiper apparatus of the opposed wiping type may have an arrangement in which a wiper driving motor is provided at the center of the vehicle and left and right wiper blades are driven in the opposing fashion as set forth above by means of a link mechanism.
However, if only one motor is employed for driving the pair of wiper blades, the drive mechanism shall have a width equal to the whole width of a vehicle for transmitting mechanical motion from the motor to both of the wiper blades. Thus, it is inevitable that the mechanism shall have a large scale and weight. If it is requested to make the mechanism small and compact, two motors may be employed for driving the left and right wiper blades.
However, if the mechanism employs two motors for driving the left and right wiper blades, respectively, the mechanism can suffer from asynchronous motions in both of the wiper blades. The asynchronous motion is caused from difference in motor drive characteristics between the left and right motors or the motor rotational rate variations due to lord imposed on the motors.
In order to avoid the above-described asynchronous motion between the left and right motors and resulting wiper motion conflict, it is a possible way to regulate the two wiper blades in such a manner that angular positions of respective wiper blades are detected and each one of the wiper blades is controlled based on its angular position relative to the other. In other words, one wiper blade is controlled so as to keep certain distance relative to the other.
However, this manner of control presupposes that the predetermined preceding-following relationship between the wiper blades are kept constantly.
Incidentally, one of the essential requirement for a wiper apparatus is to widen the wiping area to improve the view angle and view area through which a driver of a vehicle can obtain in the horizontal direction.
It is general for the wiper apparatus of the opposing type to have an arrangement in which the wiping areas of the left and right wiper blades are normally overlapped at the center portion, or a lower return position of the front glass, so as to enlarge the whole wiping area. If the wiper apparatus is made to have such arrangement, the apparatus is more stringently required to avoid the interference in motion between the pair of blades due to the asynchronous motion of the blades. Accordingly, the motors employed in the apparatus thus arranged are more stringently requested to have equal characteristics and the load variation shall be subjected to more stringent control for eliminating the interference.
Suppose that the wiper motions are controlled on the angular distance relative to the other and the wiping areas of respective wiper blades are arranged to have an overlapping area. If the preceding-following relationship between the driver's side (hereinafter referred to as DR-side) wiper blade and the assistant's side (hereinafter referred to as AS-side) wiper blade is not maintained due to any external force or the like and the wiper apparatus is still trying to recover the predetermined preceding-following relationship on the wiper blades, then the wiper blade, which shall be on the preceding side in terms of the predetermined relationship, will try to go ahead relative to the other and the wiper blade, which shall be on the following side in terms of the predetermined relationship, will try to return behind the other. The motion of the wiper blades lead to collision with each other, resulting in locking mode of the wiper apparatus stops. Consequently, if the original preceding-following relationship between the wiper blades is to be recovered, the user shall move the wiper blade manually to resume the wiping operation. In this respect, improvements have been expected.
Also, there is a case that the wiper blades are brought into contact with each other due to some factors during operation of the wiper apparatus. In this case, the system may be broken if electric conductance is continuously maintained. Therefore, electric conductance is cut off to stop the motors upon elapse of a predetermined time after the blades are locked, and the system is thus protected.
Here, the wiper blades are locked in such a case in which the relationship between the wiper blades as the preceding side and the follower side is changed due to any external force, in addition to a case of existence of an obstacle such as snow and the like. According to the control based on the positional angular distance as described above, if the relationship between the preceding side and the follower side is changed between the DR-side and the AS-side, the follower side overtakes the preceding side to maintain a normal positional angular distance, regardless of their relationship changed. That is, based on the positional angular distance between both blades, the output of the side of the blade which has overtaken is decreased and the output of the side of the other blade which has been overtaken is increased so as to return the positional angular distance to a predetermined value. Therefore, the blade which has overtaken is caught up with by the blade which has been overtaken so that both blades are brought into contact with each other. In this state, the side of the blade which has been overtaken further behaves to overtake the blade which has overtaken, and both blades are therefore locked in contact with each other.
Incidentally, suppose that each of the wiper blades is controlled based on the angular distance relative to the other and the wiper arms of the respective wiper blades are bent due to some external force in the wipe-up process, for example, with the result that positional relationship of the wiper arm, or the proximal end portion of the wiper arm, is maintained in the predetermined preceding-following relationship in spite of the fact that the actual positional relationship of the wiper blades, or distal end portion of the wiper arm, are exchanged therebetween. At this time, the preceding-following relationship between both of the blades is determined as being normal according to the control method as described above, and the replacement of the control forms as described above is not carried out. Accordingly, the locking state cannot be eliminated and also cannot be distinguished from the locking state which is caused by an obstacle, so that the motors must be stopped to turn down the system as a countermeasure.
Further, if there is snow covering the front glass, the load of the snow is almost applied to the wiper blade situated at an upper position. However, in the control system based on the positional angular distance as described above, the wiper blades tend to move with an angle difference maintained between each other, and therefore, it is possible to respond to this kind of load within the output range of only one motor. For example, when the wiper apparatus is started, only the wiper blade in the upper side operate, and therefore, it is possible to respond to the load of covering snow only within the motor output range of the upper wiper blade. In particular, in an apparatus employing a four-joint link mechanism and wiper blades are driven by the four-joint link mechanism, a large torque cannot be outputted at starting due to the nature of the four-joint link mechanism and the structure is thus weak against the load at starting. Therefore, improvements have been expected.